Automatic tensioning or braking of unwinding rolls, etc.



p 1936- L. MILLER 2,052,788

AUTOMATIC TENSIONING 0R BRAKING OF UNWINDING ROLLS, ETC

Filed May 16, 1934 Pecrv ZCQI INVENTOR.

Ll ya 6. km! BY ATTORNEYS.

Patented Sept. 1, 1936 UNITED STATES PATENT OFFICE AUTOMATIC TENSIONINGR BRAKING 0F UNWINDING ROLLS, ETC.

Lloyd E. Miller, Cleveland, Ohio, assignor to The Reliance Electric &Engineering Company, Cleveland, Ohio, a corporation of Ohio ApplicationMay 16,1934, Serial No. 725,948

3 Claims. (Cl. 242-45) means involving making physical changes in theefiort to introduce a control to maintain the tension more uniform. Inaccordance with the present invention however, tension on material froman unwinding roll or reel, or the control of a variably rotating shaftof analogous variability may be attained without manual adjustment by anoperator or recourse to physical changes by corrective devices orelectrical or mechanical relays, etc.

To the accomplishment of the foregoing and'related ends, the invention,then, comprises the features hereinafter fully described, andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawing:-

Fig. l is a semi-diagrammatic view of an embodiment of the invention;and Fig. 2 is a similar view of a modification.

A roll or other shaft S to be controlled, for instance a roll from whichmaterial is being unwound, is connected, direct or through suitablegearing, in accordance with individual circumstances, with a generator Gwhose output consists of an electrical load compensating wattage tofrequency variation. The generator for instance, may be an alternatingcurrent generator, single phase or polyphase, and in the formillustrated in Fig. 1 is a polyphase machine whose three leads Cl, C2,03 from its terminals Tl, T2, T3

'40 are provided respectively with a resistance RI and inductance LI,and resistance R2 and inductance L2, and resistance R3 and inductanceL3, connected together in Y or delta, as desired. The generator may beexcited in usual manner from a direct current source, as line D, and thedetail of the machine's design may of course vary somewhat dependingupon the particular duty involved. The generator works into a circuit ofresistance and inductance of such value as to keep the current in anyand all of the phases approximately constant. The amount of retardingeffort exerted on the reel S or the braking action provided isproportional to the watts power produced by the generator. If the powerbe main- 66 talned constant and the lineal speed of the material beingunwound is constant, then the tension on the material must be constant.As well known, the power delivered to an electric circuit is equal to PRwhere I is the effective current and R is the resistance of the circuit.That is, 5

W equals PR The current in an alternating circuit is equal to thevoltage divided by the square root of the square of the resistance plusthe square of the 10 inductance multiplied by the frequency. That is,

E I I equals Then, 15

P equals Accordingly,

R15 W equals 20 Corresponding, as an example in the case of a paperunwinding reel having connected thereto a three-phase 460 volt four-polegenerator operating at a speed of ,3600 R. P. M. to 600 25 R. P. M., aresistance value per phase may be 0.397

ohms, and inductance per phase 0.0794. Then R equals 0.1575, and Lequals 0.0063, and-such an installation is capable of maintainingapproxi mate uniformity of power for any speed within It will be seenfrom the above tabulation that the variation in power supplied does notexceed 6 per cent over the entire range of speed varia- 50 tion.

In some instances, it is desirable to take account of certain lossesoccurring in the generator, although ordinarily these are not large.Such losses are for instance those due to windage and friction and ironloss, and these increase somewhat as the speed increases. As a furtherrefinement of the invention then, I may provide for the elimination, orrather for the compensation of inequalities due to such losses. Asillustrated in Fig. 2, in relation with the shaft 8 from which thesheet-material w is being unbetween C2 and C3 is low, but it increasesas the speed increases, and by such increment it tends to prevent thevoltage in the generator from increasing in direct proportion to thespeed. The field F and its rectifier may thus eifect a reduction involtage proportionally with increase in speed, such that the sum of thedirect power produced at high speed and losses at high speed is equal tothe sum of the direct power produced at low speed and the losses at lowspeed. Close adjustment of initial setting voltagesmay be facilitated bya rheostat r in the field circuit and a rheostat r in the buckingcircuit. The connections of the terminals of the generator, and theinclusion therein of the respective resistance and inductance componentsmay be as already described foregoing. The particular values in thebucking circuit in a given case will depend upon the design of thegenerator, but as an example, in a case where the direct power producedis 8'79 watts at low speed and the losses in windage etc. '71 watts, andat high speed the direct power 930 watts and the losses 170 watts, thesum at low speed would be 879+71=950 watts, and the sum at high speedwould be 930+170=1100 watts.

.The direct power produced at high speed must or must be reduced to 91.6per cent of the value it would have had at this speed if the gnetomotive-force remained unchanged.

spears It will thus be seen that an electric load.- may be applied to ashaft to be controlled, in a manner particularly advantageous fromequipment and operating standpoint. since there is no requirement ofsupervision by an operator, nomanual control means whatsoever, nor evenany relay switches to be depended upon, with their proneness toinopportunely sticking or getting out of order. Instead, the entire unitis salt contained, the electrical load of the generator constituting theelectrical regulator, and installations may be correspondingly madeavailable in situations now handicapped by lack of space or otherconditions which have heretofore militated against extensive applicationof control means.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described-provided the featuresstated in any of the following claims, or the equivalent of such, beemployed.

I therefore particularly point out and distinctly claim as myinvention:-

1. In combination, a roll for material to be unwound, an alternatingcurrent generator connected thereto, means including resistance andinductance of selected value in circuit with said generator forautomatically controlling. to substantial uniformity the tension ofmaterial being delivered from the roll, and a bucking field winding onsaid generator and a rectifier in series therewith connected with onephase of the output circuit of the generator.

2. In combination, a rotated shaft, means for controlling the same toproduce a substantially uniform tension on material being unwound fromthe shaft and including an alternating current generator connected tothe shaft and resistance and inductance means of selected valueconstituting a circuit for said generator, and means'for supplying inthe field of said generator a rectified bucking component taken from thegenerator output.

3. Winding and reeling apparatus, comprising a rotated shaft and a pieceof material in treatment passing therefrom, means for controlling saidshaft to produce substantially uniform tension on the material throughvarious speeds of rotation, said means embodying an alternating currentgenerator having its terminals connected across a resistance andinductance of value to control the wattage substantially uniformlythrough a range 6f frequency-change, and means for compensating saidgenerator for inequalities due to the group of loss-factors includingwindage, iron loss, and friction.

LLOYD E. MILLER.

